But I live in the UK, and how on earth would I get a diagnosis?
If you see
@Max80's post on another thread
here, he explains that he could not get anyone in the NHS interested in performing this muscle biopsy, so had to go to France for the biopsy and diagnosis.
@Max80 said in that post he can provide the doctor's details.
I guess since French researchers have pioneered the study of macrophagic myofasciitis (MMF), that's where the diagnostic expertise lies. Though I would think it's worth enquiring in the UK NHS first.
However, I am not sure whether or not macrophagic myofasciitis can appear within days of vaccination, like the 1-day timescale of your post-vaccination ME/CFS symptoms.
This study finds that that the onset of MMF occurred an average of 7 months after vaccination:
As previously reported, onset of these clinical symptoms was always posterior to, and delayed from, immunization, median time elapsed from last vaccine administration being 7 months (range 0.5–84) for initial systemic symptoms, and 11 months (range 0–72) for first myalgia.
They say the fastest onset they encountered was 0.5 months (two weeks). So you might want to investigate whether the 1 day time to onset is compatible with MMF, or whether this is just too fast.
Maybe because you were sort of predisposed to getting ME/CFS (having had ME/CFS symptoms earlier in your life), that's why the MMF appeared so quickly (if you do have MMF)?
Interestingly enough, the study also mentions that:
It is now clear that rapid emergence of MMF in France resulted from the specific combination of 3 factors : (1) replacement of the subcutaneous route by the i.m. route of vaccination in the early 1990s; (2) widespread extension of HBV primovaccination to the French adult population in the same time; and (3) the choice of the deltoid muscle (also used for i.m. vaccination) for routine muscle biopsy in France whereas biceps brachialis and quadriceps femoris muscles are preferred in most other countries.
So I am guessing that MMF tends only occur from intramuscular injection, not by subcutaneous injection.